Agents later intercepted the semi-submersible, on which they
found more than 12,800 pounds of cocaine, an amount with an
estimated value of $193,939,000, according to a CBP release issued on
March 24. US agents arrested four people operating the craft.

The seizure was short-lived however, as the "semi-submersible
became unstable and sank," the CBP said in a release. Semi-submersible crafts used
for drug smuggling are also referred to as "narco submarines."

Despite losing the cargo, the CBP characterized the operation as
a success. "Our crews will continue to take every opportunity to
disrupt this type of transnational criminal activity," said John Wassong, the director of the
National Air Security Operations Center in Corpus Christi, Texas.

Semi-submersibles used for smuggling are usually built to travel
just below the surface, with just an exhaust pipe, a wheelhouse,
and an airstack emerging from the water, according to Vice News. The vessels are often
camouflaged, and many of them are constructed in Colombia, a major hub for cocaine production.

A semi-submersible
transporting drugs was captured at sea last year by US agents,
but it sank before it could be fully unloaded.US Customs and Border Patrol

"Typically crews are made up of an experienced sailor, the
so-called "captain" who can also be the person who handles
communication with the 'base,'" Javier Guerrero, a researcher
focused on drug-trade technology, told Vice in 2015. "Most likely
the crew is made up of experienced sailors," as well, said
Guerrero, and their experience and relationship with the cargo's
owner or the narco sub's owner determines the command hierarchy
on the vessel.

The emphasis traffickers have put on seaborne smuggling is
one of the latest logistical and technical developments in the
drug trade. Throughout much of 1970s and 1980s, most trafficking
routes, via air and sea, transited the Caribbean. As interdiction
efforts increased, smugglers switched to land and air routes through
Mexico, eventually branching into more intense maritime
smuggling.

"They started to build the
submarines and they're still using them, but it's aircraft,
commercial freighters, speedboats. You name it and they have it,"
Mike Vigil, the former chief of international operations for the
DEA, told Business Insider. "They never settle on one method of
transportation or on one route. They're always exploring."

Counternarcotics
police guard an under-construction submersible that was seized
from the "Los Urabenos" drugs cartel, in Puerto Escondido,
Monteria province October 18, 2011. Colombian authorities said
that the submersible ship seized on Monday could be used to carry
six tons of cocaine illegally.REUTERS/John Vizcaino

In 2012, 80% of the illegal drugs
smuggled to the US came on maritime routes, and 30% of the
illegal drugs delivered to US shores via the sea were carried on
narco submarines, according to a 2014 study cited by Vice News.

In late summer last year, US
agents intercepted a semi-submersible laden with
roughly eight tons of cocaine. US authorities offloaded about six
tons of the illicit cargo before the vessel sank. The capture and
subsequent sinking of the narco sub were recorded by the Coast Guard.

Had US agents been able to bring this latest shipment to shore,
it would have been one of the more substantial hauls captured in
recent months. In early February, Air and Marines Operations
agents intercepted a 2,300-pound shipment with an
estimated value of $172 million. In early March, CBP agents
caught a 154-pound shipment in Fort Lauderdale,
Florida, which had an estimated value of $2 million.

Air and Marine Operations agents took part in 198 seizure,
disruption, or interdiction efforts in their 42-million-square-mile operation zone — which
spans the Pacific Ocean, Caribbean Sea, and the Gulf of Mexico —
in fiscal year 2015, capturing over 200,000 pounds of cocaine.